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Groundwater pumping causing levels to rapidly drop

Thanks to a severe, multiyear drought and increased demand for water, groundwater levels in the Upper Rio Grande Basin in Colorado, New Mexico and Far West Texas have dropped as much as 200 feet through the years.

A water expert at New Mexico State University (NMSU) warns those levels are just the tip of the iceberg as a sluggish recharge of the river, combined with increased groundwater pumping in the years ahead, will create worse shortages in the near future.

Brian Hurd, an agricultural economics professor and president of the Universities Council on Water Resources was quoted recently in the El Paso Times, saying that the threat of coming water shortages in New Mexico and Texas represents a serious problem for farmers up and down the entire basin region.

"The real big deal is going to be the change in the intensity of pumping," Hurd told the Times (http://bit.ly/1ricO5E).

Hurd and government hydrologists agree that river flows in the Rio Grande will suffer more as the demand for groundwater increases as a result of growing population density and the need for more water for agricultural and industrial activities.

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In a 2013 joint Upper Rio Grande Impact Assessment prepared by the U.S. Department of the Interior's Bureau of Reclamation, the U.S. Army Corp of Engineers and the Sandia Laboratory Climate Security Program, even at the current annual use of groundwater throughout the Basin, critical water shortages will intensify in the years ahead.

According to that assessment, in the Upper Rio Grande Basin of Colorado and New Mexico, water management challenges posed by a highly variable and extremely limited water supply have been exacerbated by a prolonged drought.

In addition to problems associated with heavy groundwater pumping, the assessment determined that pronounced changes in climate in future years are anticipated for the Upper Rio Grande. The climate modeling used to support the study suggested that average temperatures in the Upper Rio Grande Basin may rise by an additional 4 degrees to 6 degrees F by the end of the 21st century.

Simulations

These model simulations do not consistently project changes in annual average precipitation in this basin, but they do project changes to the magnitude, timing, and variability of inflows to the system. In addition to groundwater demand, the study detailed the following:

Decreases in overall water availability

Supplies of all native sources to the Rio Grande are projected to decrease on average by about one third, while flows in the tributaries that supply the imported water of the San Juan-Chama Project are projected to decrease on average by about one fourth.

Changes in the timing of flows

The seasonality of flows is projected to change. Anticipated changes include earlier snowmelt runoffs as well as increased variability in the magnitude, timing, and spatial distribution of streamflow and other hydrologic variables. Projections indicate that this basin will experience a decrease in summertime flows and less of a decrease (or potentially even an increase) in wintertime flows.

Increases in the variability of flows

All simulations used in this study project an increase in the month-to-month and inter-annual variability of flows over the course of the century. The frequency, intensity, and duration of both droughts and floods are projected to increase.

While climate change will increase the risks of water shortage in the basin area, of more immediate concern is how communities and industry will react to current shortages. While recent drought conditions have lowered reservoir levels and decreased inflows to lakes, increased pumping of groundwater has helped to sustain adequate resources in the short term.

Challenges ahead

But hydrologists say the time for such groundwater relief may be short lived as demand increases and groundwater levels continue to drop.

Zhuping Sheng, a hydrologist at the Texas A&M AgriLife Research and Extension Center in El Paso, draws a comparison with putting money in the bank.

"We're withdrawing more than we are depositing," he says.

He points out that in some areas around El Paso, for example, groundwater levels have dropped by as much as 200 feet over the last century.

Hydrologists say as groundwater continues to diminish as a result of slower recharge and greater use, population levels along the basin are expected to rise, adding a greater strain on the region's hydrology.

Adding to the overall problems are both the ongoing drought and lighter-than-normal snowpacks in the San Juan mountains in recent years. Water experts say significant and beneficial rains over the last two summer and fall seasons have helped, but it was "like putting a Band-Aid on a major wound."

As farmers prepare for planting in 2015, concerns are elevated over whether there will be enough water to bring their crops to another successful harvest. Good rains in the second half of this year should provide enough water to get the crop started, but experts say another dry summer could be devastating if those rains don't continue late into the growing season.